The invention relates to an oil measurement device for determining and/or monitoring the temperature and/or the quality of oil situated in a tank.
The invention also relates to a method for monitoring oil situated in a tank. Here, depending on the application, various parameters may be of interest for the monitoring, such as for example the temperature and quality of the oil or for example the number and/or duration of heating cycles that the oil undergoes during use.
In the prior art, it is for example possible to find numerous household and/or catering devices which have tanks, in particular electrically heatable tanks, which are filled with liquid oil or grease during operation. In large kitchens in particular, use is made for example of positionally fixed deep fryers in which preferably continuous monitoring of the temperature of the liquid oil or grease and, at regular intervals, measurement of the quality of the oil or grease are necessary for food hygiene reasons.
With regard to deep fryers, conventional devices for example offer the possibility of monitoring the quality of the frying oil during operation. For this purpose, a return line is typically provided between a frying tank and a filter tank, with a sensor being provided either in the return line or in a branch from the return line in order to check the quality of the oil that is pumped back.
For deep fryers in particular, measurement systems are thus known from the prior art which have sensors which are installed in positionally fixed fashion in the wall of a tank which accommodates the oil or in a filter circuit of the oil which is connected to said tank.
Such measurement systems cannot be removed from the device without relatively great structural modifications. Therefore, such non-modular systems in particular do not offer the possibility of a measurement functionality as described in the introduction being retrofitted with little effort to existing deep fryers without fixedly installed sensors. With existing systems, such retrofitting is cumbersome and expensive and, in the case of these, there is also no provision made for monitoring multiple tanks simultaneously or in flexible fashion.
There is however an increased demand for specifically such retrofittability and flexible monitoring because, firstly, the demands with regard to the monitoring of food hygiene are ever-increasing and, secondly, high costs for retrofitting or new procurement of devices must be avoided for economic reasons.
Typical processes which influence the quality of the oil, or more specifically the quality of the mixture of liquid oil or grease and other substances situated therein, are the breakdown of oil molecules and the absorption of water. Both processes generally lead to a change in the electrical characteristics of the oil, in particular to an increase of the electrical permittivity ∈ of the oil, which is also referred to as dielectric conductivity.
It is known that the quality of the oil, that is to say in particular the purity of the oil and the water content in the oil, can be inferred by a measurement of the permittivity ∈ of the oil.
To be able to make reliable statements regarding the quality of the oil on the basis of a measurement of the permittivity ∈, a parallel temperature measurement is however necessary because, in the event of a temperature increase, water evaporates out of the oil, and therefore reliable statements can be made only after the evaporation.